A sophisticated Trojan designed to empty bank accounts has a new trick up its sleeve: It lies to investigators about where the money is going.

A sophisticated Trojan designed to empty bank accounts has a new trick up its sleeve: It rewrites bank statements to disguise where the money is going.

First uncovered by Finjan Software, the URLzone Trojan is already known to be very advanced. It rewrites bank pages so that the victims don't know that their accounts have been emptied, and it also has a sophisticated command-and-control interface that lets the bad guys pre-set what percentage of the account balance they want to clear out.

But Finjan isn't the only company looking into URLzone. RSA Security researchers say the software uses several techniques to spot machines that are run by investigators and law enforcement. Researchers typically create their own programs that are designed to mimic the behavior of real Trojans. When URLzone identifies one of these, it sends it bogus information, according to Aviv Raff, RSA's FraudAction research lab manager.

Security experts have long published research into the inner workings of malicious computer programs such as URLzone, Raff said. "Now the other side knows that they are being watched and they're acting," he said.

When URLzone spots a researcher's program, instead of simply disconnecting from the researcher's computer, the server tells it to do a money transfer. But instead of transferring the money into one of the criminal's money mules -- people who have been recruited to move cash overseas -- it chooses an innocent victim. Typically, these are people who have received legitimate money transfers from other hacked computers on the network, Raff said.

So far, more than 400 legitimate accounts have been used in this way, RSA said.